The terms that come up most often in fab notes, DFM reports and assembly drawings — in plain language.
| Term | Definition |
|---|---|
| Annular ring | The copper ring around a drilled hole that connects the pad to the barrel. |
| Aspect ratio | Board thickness divided by drill diameter; higher ratios are harder to plate reliably. |
| AOI | Automated optical inspection: camera-based comparison of the board against a programmed model. |
| BGA | Ball grid array: a package with solder balls underneath, inspected by X-ray. |
| Blind via | A via that connects an outer layer to an inner layer without passing through the board. |
| Buried via | A via that connects inner layers only and is not visible on either surface. |
| Centroid file | Pick-and-place data with component reference, X/Y position, rotation and side. |
| Controlled impedance | Design and fabrication of traces to a specified impedance, verified with coupons. |
| DFM | Design for manufacturing: checking a design against the fabrication process window. |
| DFA | Design for assembly: checking component spacing, access, fiducials and panel handling. |
| ENIG | Electroless nickel immersion gold: a flat, solderable surface finish. |
| FAI | First-article inspection: documented verification of the first board against the drawing and BOM. |
| Fiducial | A copper dot used by the placement machine to locate the board precisely. |
| HASL | Hot air solder levelling: a tin-lead or lead-free finish, less flat than ENIG. |
| HDI | High-density interconnect: finer traces, smaller vias and sequential lamination. |
| ICT | In-circuit test: checks component presence, value and orientation on an assembled board. |
| MSL | Moisture sensitivity level: how long a component can be exposed before reflow requires baking. |
| OSP | Organic solderability preservative: a thin, flat, cost-effective finish. |
| Panelization | Arranging multiple boards on a production panel with rails and break-away features. |
| Rigid-flex | A board that combines rigid and flexible sections in one construction. |
| Solder mask | The protective polymer layer that defines exposed copper and prevents bridging. |
| SPI | Solder paste inspection: 3D measurement of paste volume and alignment before reflow. |
| Tg | Glass transition temperature: the point where laminate softens and expands more rapidly. |
| Via-in-pad | A via placed inside a component pad, usually filled and planarized for assembly. |
A term missing from this list? Ask us and we will explain how it applies to your build — and add it to the glossary.